A Vegetable Matter: Separating the Wool from the Chaff

Most sheep spend most of their lives outdoors, sleeping on the ground, browsing the local grasses and weeds. When they are brought indoors for lambing or for shelter from the weather, they typically sleep on straw and eat hay. No matter how well cared for they are, sheep and other fiber animals collect dried grasses, twigs, and seeds in their fleece. This plant debris is referred to as vegetable matter (VM).

While VM is both natural and, to some extent, unavoidable, you probably don’t want to find it in your yarn. Excessive VM will make your finished project “scratchy” and uncomfortable to wear, no matter how soft the wool itself. Let’s look at how VM is removed from wool at various stages along the road from farm to skein. We’ll also discuss what you can do when you encounter VM in your yarn.

At the Farm

Removal of VM begins as soon as the fleece leaves the sheep. The belly wool, which collects VM (along with lots of dirt) when the sheep lays down to sleep, is immediately removed and discarded or set aside for other uses. The fleece is often then thrown, cut side down, onto a skirting table. The skirting table has a top made of metal mesh or wooden slats, allowing dirt and debris to fall to the ground.

Skirting a fleece takes place at Ranching Tradition Fiber in southwest Montana. Photo courtesy of Kami Noyes of Ranching Tradition Fibers

All the dirtiest parts of the fleece are removed, including any sections with heavy VM contamination. The fleece is then rolled and bagged or baled for transportation to the wool mill.

At the Mill

Scouring
When the raw wool arrives at the mill, the first step is a thorough washing. While the type and size of washing equipment might vary, the process generally involves two or three passes through hot water dosed with detergent and some very gentle agitation. This scouring removes some, but not all, of the VM.

Carbonizing
Wool that is destined for woolen spinning may be carbonized immediately after washing to remove any remaining VM. VM is primarily cellulose, which is made up of carbon and water. The carbonizing process involves immersing the wool in a sulfuric acid solution, which breaks the bonds between the water and the carbon in cellulose. The wool is then dried at 140–176°F (60–80°C) to remove the water and baked at 203–248°F (95–120°C) to make the remaining VM brittle. A pass between rollers[PAYWALL] crushes the carbonized VM and a rotating shaker removes the charred dust. The wool (now free of virtually all VM) is immersed in a neutralizing solution and a final rinse.

For obvious reasons, carbonizing is not performed at small wool mills. Most carbonizing occurs in mills in Australia, South Africa, and Asia. Fine wools, such as superfine Merino, can be damaged by the acid used in carbonization. Failure to properly control acid concentration and drying temperatures can result in wool that is brittle.

Wool that has been carbonized cannot be certified organic under the Global Organic Textile Standard (GOTS).

After the wool has been washed and dried (and perhaps carbonized), it needs to be prepared for spinning. This is accomplished with either carding or combing.

Carding
The clean, dry wool will next be carded to open the locks and separate the fibers. The carder is a series of rollers covered with small metal teeth. The rollers move at different speeds, allowing the teeth to pick apart any clumps and open the mass of wool as the fiber moves from roller to roller. Much of the VM that remains after washing will fall away from the wool during carding.

Some of the carding machinery is shown at Skagit Woolen Works in Mount Vernon, Washington. Photo courtesy of Skagit Woolen Works

Combing
If the wool is destined for worsted spinning (as opposed to woolen), combing is the next step. The carded wool is pulled through a series of fine-toothed metal combs to align the fibers. Combing also removes any short or irregular fibers, along with nearly all remaining VM. Worsted-spun wool is rarely carbonized, since combing makes the extra treatment unnecessary.

Spinning
By the time the wool reaches the spinners, any VM that remains is likely to be both small and tenacious. Bits of hay or straw may be dislodged during twisting, but those stubborn little burs may only become further embedded in the yarn.

At Home

If you’re a regular reader of Farm & Fiber Knits, you know we are fans of minimally processed, close-to-the-farm wool. We also appreciate the lightweight insulation created by lofty, woolen-spun yarns. That means we sometimes find VM in our skeins of yarn.

A close look at this skein shows small bits of VM. Photo courtesy of Devin Helmen

Personally, I don’t fret about the occasional bit of VM. My rule of thumb is this: If it pokes my fingers while I’m knitting, I take the time to pick it out of the yarn. Otherwise, I simply ignore it.

You may be more sensitive to the occasional prickle or be knitting for someone who is. In that case, you’ll have no trouble finding yarns which have been worsted spun from combed wool and are virtually free of VM. Due to consumer demand for “soft” yarns, much of the yarn on the shelves of your local yarn store are worsted spun. If you do encounter the odd bit of straw, let it remind you of the sheep that grew your wool and the land which nurtured her. Then simply pick it out. Your fingertips are a better tool than all the machinery in any mill!

Resources

Westmoreland, David. “Wool Carbonising.” Australian Wool Education Trust. woolwise.com

Special thanks to the following for providing images for this article:
* Kami Noyes, Ranching Tradition Fiber
* Skagit Woolen Works
* Devin Helmen